Key attestation的几个关键点！

Key attestation就是密钥认证，之前介绍过：

Key attestation-Google的密钥认证

下图是Google Android密钥认证的架构图。基本上TEE OS、Keystore、Keymaster等等都有相关涉及。

我们今天来总结一下密钥认证的几个关键点：

Attestation details

● 认证可以应用于RSA或EC密钥。

● 证书是以X.509证书的形式出示的。

● 认证密钥（ECDSA和RSA）将设置在工厂。

● 谷歌将提供CA根，并将认证密钥。

Key Provisioning

● 谷歌将为谷歌批准的设备认证认证密钥。

● 密钥将被部署到设备上，每10K设备用一个密钥。

● 谷歌将创建密钥并对它们进行验证。

这个过程是与Widevine密钥分配过程非常类似（将可能使用相同的交付方法）。

密钥撤回：密钥撤销将通过CRL和OSCP被取消

● 安全密钥注入只能在工厂完成，所以设备被吊销的密钥将永久不受信任。

● 密钥被注入到设备批次中，因此撤销至少影响整个批处理。

● 撤销将应用广泛的需要，根据泄漏的性质和范围。

其他的keystore安全措施：

● More elliptic curve functionality：ECIES ECDH

● Exportable symmetric keys

● Fingerprint-bound keys that are not revoked on fingerprint enrollment

● OS version binding to protect against OS rollback

Bootloader修改：

新的硬件密钥库功能需要一些BootLoader功能：

● Bootloader must provide OS version and patch level to TEE.

● Bootloader must provide Verified Boot public key and lock status to TEE.

CDD测试要求：

Hardware-backed keystore will be MANDATORY in a future release.

● All algorithms (RSA, AES, ECDSA, ECDH, ECIES, HMAC)

● All hash functions (MD5, SHA1, SHA-2 family)

● Hardware Gatekeeper (on devices with lockscreens)

● With brute force protection in hardware

● Hardware attestation support

FIDO and Android KeyStore Attestation

KeyStore attestation is similar to—but not an implementation of—FIDO U2F.

● U2F uses other data structures and protocols that are too specific for a

general-purpose crypto toolkit.

● KeyStore attestation does provide all of the security properties desired by

FIDO relying parties.

● Google will work with FIDO to reconcile the issues.

● Bottom line: FIDO relying parties will be able to use KeyStore. This is

expected to drive widespread use of KeyStore.